1. Field of the Invention
The invention relates to a projection exposure device which is used, for example, for production of a semiconductor device, a printed board, an LCD (liquid crystal display), and for similar purposes. The invention relates more specifically to a process for exposure in which positioning of alignment marks which are located on the back of a workpiece is performed relative to alignment marks of a mask, and in which projection exposure of a mask pattern onto the workpiece is produced. The invention also relates to a device for executing such a process.
2. Description of Related Art
In the production of a power transistor, micro machine, printed circuit board and the like, it is important to expose the pattern of a mask exactly in a predetermined position of a workpiece, such as a silicon wafer, epoxy resin and the like. The above described positioning is conventionally performed in such a way that the alignment marks of the mask and workpiece come to rest on top of one another. In particular, in a certain production process, there are cases in which the pattern is burned onto both sides of a workpiece, exact positioning of one pattern on the front side relative to the other pattern on the back being important.
This means that, in the formation of the back pattern, by turning over the workpiece with the pattern formed on its front and then exposing the back, it is necessary that alignment marks which are recorded on the front surface, on which the pattern is already formed and which are positioned by turning to the back relative to the surface exposed to the mask alignment marks, and that the pattern on the back be positioned relative to the pattern of the front. (In the following, this alignment is called back alignment).
In a process of manufacturing a micro machine, there is a need for accuracy of the above described positioning equal, for example, to roughly 1 micron.
The above described back alignment is conventionally used only for a proximity printing system in which the mask and the workpiece are caused to approach one another and exposure is produced. It is not used in a projection exposure system in which the mask pattern is projected onto the workpiece via a projection lens and exposure is performed.
The projection exposure system was conventionally used for working in the micro domain, such as formation of chips on a wafer surface, as in a reduction projection exposure device of the stepper type.
On the other hand, recently, exposure of both sides of the workpiece has been performed more and more often, as in a process of manufacture of a micro machine and the like. In this case, a double-side type of exposure is used more and more frequently in which, for example, one surface of the workpiece is subjected to precision processing by exposure by means of a stepper or the like, in which, then, the workpiece is turned, alignment of the second surface is performed using the alignment marks on the back surface and then exposure is performed.
To date, the proximity printing system as was described above was conventional as the exposure system for double-sided exposure by executing back alignment. In the proximity printing system, however, it was considered to be a disadvantage that impurities or the like which are formed on the workpiece and the mask cause faults, in this case, because the mask and the workpiece are caused to approach one another and exposure is done.